The art of monitorinq and responding to changes in the chemical make-up of an aqueous medium has traditionally included various and sometimes diverse methods. Of particular interest herein are the methods used to monitor the aqueous, sometimes called brine, effluent from the desalter operation of a petroleum refinery.
Crude oil desalting is a common emulsion breaking application where the emulsion is first intentionally formed. Water is added in an amount of approximately between 3% and 8% by volume of crude. The added water is intimately mixed with the crude oil to contact the impurities therein, thereby transferring these impurities into the water phase of the emulsion. The emulsion is usually resolved with the assistance of emulsion breaking chemicals, which are characteristically surfactants, and by the known method of providing an electrical field to polarize the water droplets. Once the emulsion is broken, the water and petroleum media form distinct phases. The water phase is separated from the petroleum phase and subsequently removed from the desalter. The petroleum phase is directed further downstream for processing through the refinery operation.
The efficiency of the desalting operation is, in part, dependent upon the proper handling of the emulsion. A precise amount of emulsion breakers is essential. Specifically, either too little or too much breaker can stabilize an emulsion. This is characterized by increased opaqueness of the effluent. Common contemporary devices monitor the level of opaqueness of the brine effluent. However, this method does not differentiate between undertreatment and overtreatment. This can result in serious operational problems. An improper reading of the emulsion could result, for example, to the addition of more emulsion breakers to an emulsion already overtreated which would, in turn, lead to further emulsion stabilization and loss of system control.